The present invention relates to closed cycle gas refrigerating equipment capable of generating a cooling effect for uses in which low temperatures (lower than 100.degree. K.) on small surfaces are required.
Devices are known which produce such an effect. Among these known devices, some obtain the cooling action by virtue of gas working against a piston; other known devices obtain the same effect through gas expansion by virtue of an evacuating and pressurizing compressor. All of these devices are provided with a heat exchanger inside the piston.
The object of the present invention is an improved device for obtaining the foregoing purposes, in which the refrigeration is obtained by combining the two above stated principles. Therefore, a closed cycle cooling apparatus according to the present invention is capable of producing very low temperatures (lower than 100.degree. K.). The apparatus is characterized in that it completes a combined cycle with both gas expansion and gas working against a piston, and expansion by means of an evacuating compressor system. In a preferred embodiment the piston on which the expanding gas acts is used to act on the piston shaft motor, so that the work effected by the gas during expansion accelerates the motor which acts as a brake, accumulating energy for a subsequent phase in which the piston lowers again. The piston may have a shaft extending from the previously compressed gas expansion region, and the shaft together with the control unit is placed in a region at the low pressure provided by the evacuating compressor. In this low pressure area the delivery valves open, and the area compensates the differences occurring between the cryogenic unit gas input rate and the evacuating unit suction rate.
A piston against which the gas works is separated from the outer cylinder by means of an annular cavity extending from the room temperature area to the cryogenic temperature.
A one-stage piston may include an axial passage to permit gas inlet and outlet. A two-stage piston may also have an axial passage to allow gas inlet and outlet.
The invention will be better understood in connection with the specification to follow and the annexed drawings; which show a non-limitative embodiment of the invention itself.